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  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
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  • B01J35/64—Pore diameter
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  • B01J35/64—Pore diameter
  • B01J35/657—Pore diameter larger than 1000 nm
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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  • B01J37/0236—Drying, e.g. preparing a suspension, adding a soluble salt and drying
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  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0078—Composite solid storage mediums, i.e. coherent or loose mixtures of different solid constituents, chemically or structurally heterogeneous solid masses, coated solids or solids having a chemically modified surface region
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  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0084—Solid storage mediums characterised by their shape, e.g. pellets, sintered shaped bodies, sheets, porous compacts, spongy metals, hollow particles, solids with cavities, layered solids
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  • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
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  • C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof
  • C01B6/06—Hydrides of aluminium, gallium, indium, thallium, germanium, tin, lead, arsenic, antimony, bismuth or polonium; Monoborane; Diborane; Addition complexes thereof
  • C01B6/10—Monoborane; Diborane; Addition complexes thereof
  • C01B6/13—Addition complexes of monoborane or diborane, e.g. with phosphine, arsine or hydrazine
  • C01B6/15—Metal borohydrides; Addition complexes thereof
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  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
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  • C04B35/524—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from polymer precursors, e.g. glass-like carbon material
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
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  • C04B41/51—Metallising, e.g. infiltration of sintered ceramic preforms with molten metal
  • C04B41/5111—Ag, Au, Pd, Pt or Cu
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/48—Organic compounds becoming part of a ceramic after heat treatment, e.g. carbonising phenol resins
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/32—Hydrogen storage
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

• the present invention relates to a macroporous monolithic composite material, in particular to a carbon monolith with a hierarchical porous structure comprising metallic nanoparticles, and to its preparation process, to a hydrogen storage method implementing it. , to a process for producing gaseous hydrogen using such a composite material, said process being reversible.
• porous carbon monoliths Materials in the form of porous carbon monoliths are materials of choice for many applications such as water and air purification, adsorption, heterogeneous phase catalysis, electrode fabrication and energy storage due to their large surface area, large pore volume, insensitivity to surrounding chemical reactions and excellent mechanical properties.
• These materials comprise a high specific surface and a hierarchical structure, that is to say a honeycomb structure generally having a double porosity. They have in particular a mesoporous structure in which the average pore diameter varies from about 2 to 10 nm.
• the storage and production of dihydrogen is a major issue today due to the evolution of technologies and the depletion of oil resources.
• the craze for wearable technologies is generating a growing demand for systems that allow the storage and production of dihydrogen in a simple and industrializable way.
• LiBH 4 lithium borohydride
• the object of the present invention is to provide a material from which it is possible to produce dihydrogen in a simple and reversible manner at temperatures lower than those which are usually necessary to obtain desorption of hydrogen in the form of dihydrogen from a metal borohydride and it is further possible to rehydrogenate under acceptable conditions of temperature and pressure.
• the inventors have in fact developed a material in the form of a carbon monolith with a hierarchical porous M2 structure (Macroporous / Microporous) comprising nanoparticles of a suitably selected metal and which can advantageously be used for storage.
• a material in the form of a carbon monolith with a hierarchical porous M2 structure (Macroporous / Microporous) comprising nanoparticles of a suitably selected metal and which can advantageously be used for storage.
• hydrogen by heterogeneous nucleation of a metal hydride in the porosity of said monolith, as well as for producing dihydrogen by desorption of the hydrogen contained in the composite material resulting from the hydrogen storage process, said material can then be rehydrogenated.
• the present invention therefore has for first object a cellular solid composite material is in the form of a porous carbon monolith having a hierarchical porous network comprising macropores having an average dimension of 1 A ⁇ to about 100 ⁇ , preferably About 4 to about 70 ⁇ , and micropores having a mean dimension di from 0.7 to 1.5 nm, said macropores and micropores being interconnected, said material being free of mesoporous network and being characterized in that it comprises nanoparticles a metal M of zero oxidation state, said metal M being selected from palladium and gold.
• the palladium or gold nanoparticles are present on the surface and in the monolith of the monolith. More precisely, the nanoparticles of palladium or gold are present on the surface of the macropores of the monolith.
• the size of the metal nanoparticles M may vary from about 1 to 300 nm. According to a preferred embodiment of the invention, the size of the metal nanoparticles M varies from 2 to approximately 100 nm and more particularly from approximately 2 to 20 nm.
• the term "monolith” means a solid object having an average dimension of at least 1 mm.
• mesoporous network is understood to mean a network comprising mesopores, that is to say pores whose size varies from 2 to 50 nm.
• the walls of the macropores generally have a thickness of 1 to 10 nm, and preferably 1 to 20 nm.
• the micropores are present in the thickness of the walls of the macropores, thus rendering them microporous.
• the specific surface area of the material according to the invention is generally from 50 to 900 m 2 / g approximately, preferably from 100 to 700 m 2 / g approximately.
• the presence of these metal nanoparticles in the carbon monoliths makes it possible to greatly improve the rehydrogenation process, thus making it possible to access a reversible storage method of the hydrogen at 400 ° C.
• the inventors of the present application have not yet clearly identified the mechanism which is the basis of this improvement, but they think that it is not a catalyzed rehydrogenation reaction since no catalytic reduction of boron by metals has not yet been reported in the literature.
• Another subject of the invention is a process for preparing a composite material as described above, said process comprising the following steps: i) a step of impregnating a porous carbon monolith comprising a hierarchical porous network comprising macropores having a mean dimension d A of from about 1 ⁇ to about 100 ⁇ , preferably from about 4 to about 70 ⁇ , and micropores having a mean dimension di from 0.7 to 1.5 nm, said macropores and micropores being interconnected said material being free of mesoporous lattice by a solution of a salt of a metal M selected from palladium and gold in a solvent;
• Steps i) to iii) can of course be optionally repeated one or more times depending on the final amount of metal nanoparticles that it is desired to incorporate into the carbon monolith and the concentration of the metal salt solution used to achieve impregnation.
• the carbon monoliths that can be used in step i) of the process according to the invention ("bare" monoliths) are materials that are known per se and whose preparation method is described, for example, in the FR-A1 patent application. -2,937,970.
• the salts of the metal M is not critical.
• the salts of a metal M that can be used according to the process according to the invention can in particular be chosen from chlorides, sulphates, nitrates, phosphates, etc.
• the nature of the solvent of the salt solution of the metal M is not critical from the moment it makes it possible to solubilize said metal M.
• the solvent of the metal salt solution M is a polar solvent selected from water, lower alcohols such as methanol and ethanol, acetone, etc., and mixtures thereof.
• the metal M salt concentration in the impregnating solution preferably ranges from 10 "3 M to 1 M and even more preferably from 10" 2-10 "1 M.
• Step ii) drying the monolith is preferably carried out at a temperature of 20 to 80 ° C, and more preferably at room temperature.
• the nature of the reducing gas used during step iii) of forming the metal nanoparticles M is not critical insofar as it makes it possible to reduce said metal M to the zero oxidation state.
• the reducing gas may in particular be chosen from hydrogen, argon, etc., and mixtures thereof; hydrogen being particularly preferred.
• the heat treatment step iii) is carried out at a temperature of about 80 to 400 ° C.
• the heat treatment of step iii) is carried out in the presence of hydrogen at a temperature of about 400 ° C. for 1 hour.
• the composite material according to the invention and thus prepared can then be used for the storage of hydrogen.
• the subject of the invention is therefore also a process for storing hydrogen in a composite material comprising nanoparticles of a metal M selected from palladium and gold at zero oxidation state according to the invention and as described above, said method being characterized in that it comprises at least the following steps:
• the degassing of the material during step a) is carried out at a temperature of about 280 to 320 ° C. and even more preferably at a temperature of about 300 ° C.
• step a) can vary from about 2 to 24 hours, it is preferably about 12 hours.
• the formula (I) of the metal hydrides that may be used according to the invention naturally includes lithium borohydride (Li (BH 4 )), sodium borohydride (Na (BH 4 )) and magnesium tetrahydroboride (Mg (BH 4 ) 2 ) and potassium borohydride (K (BH 4 )).
• lithium borohydride is particularly preferred.
• the ether solvents that can be used during step b) can be chosen from aliphatic ethers and cyclic ethers.
• aliphatic ethers alkyl ethers there may be mentioned such as methyl Tertz 'obutyléther (MTBE) or diethyl ether.
• MTBE Tertz 'obutyléther
• cyclic ethers there may be mentioned tetrahydrofuran.
• the solvent of the metal hydride solution is MTBE.
• the concentration of the metal hydride solution of formula (I) used in step b) preferably varies from 0.05 to 5 M, and still more preferably from 0.1 to 0.5 M approximately.
• the specific surface area of the composite material according to the invention is generally from 50 to 900 m 2 / g approximately, preferably from 100 to 700 m 2 / g approximately.
• the micropore volume is greater than or equal to 0.30 cm 3 • g -1 of composite monolith and the metal hydride of the formula (I) in this case is in amorphous form.
• the content of hydrogen present in the form of metal hydride in the composite material according to the invention will vary according to the microporous volume and the specific surface area of the monolith used during the impregnation step b) and the hydride concentration. metallic solution used for impregnation of said monolith.
• the hydrogen content varies from about 0.01 to about 0.03 moles of hydrogen per gram of monolithic carbon. This molar amount corresponds to a specific capacity of 1.8 to 5.4% (mass of hydrogen stored relative to the total mass of the composite material).
• the subject of the invention is the use of a composite material as defined above for the production of dihydrogen, in particular to provide dihydrogen in a fuel cell operating with dihydrogen.
• the invention relates to the process for producing dihydrogen using a composite material according to the present invention. It is characterized in that the composite material as defined above is subjected to a heating step at a temperature of at least 100 ° C. Preferably, the heating step is carried out at a temperature of 250 to 400 ° C.
• the evolution of dihydrogen is observed following the desorption of hydrogen from the metal hydride of formula (I) contained in the micropores of the composite material according to the invention.
• the composite material according to the invention has the particularity of being able to be rehydrogenated.
• the composite material is subjected to a hydrogen pressure of 50 to 200 bar at a temperature of 200 to 500 ° C for 1 to 48 hours.
• the subject of the invention is a reversible process for producing dihydrogen using a composite material containing a metal hydride of formula (I) according to the present invention and as defined above, said process being characterized in that it includes the following steps:
• step 2) is carried out by subjecting the material to a hydrogen pressure of 100 bar at 400 ° C for 12 to 24 hours.
• the present invention is illustrated by the following exemplary embodiments, to which it is however not limited.
• Tetrahydrofuran (THF); - 37% hydrochloric acid; 50% hydrofluoric acid: Carlo Erba Reagents;
• the macroporosity was qualitatively characterized by a scanning electron microscopy (SEM) technique using a Hitachi TM-1000 scanning microscope that operates at 15 kV.
• SEM scanning electron microscopy
• the samples were coated with gold and palladium in a vacuum evaporator prior to their characterization.
• the mesoporosity was characterized qualitatively by a transmission electron microscopy (TEM) technique using a Jeol 2000 FX microscope with a 200 kV acceleration voltage. The samples were crushed into powder form which was then placed on a copper grid coated with a Formvar & Commat carbon membrane.
• TEM transmission electron microscopy
• XRD diffraction analysis
• the desorption of hydrogen was followed by volumetric measurements using a Sieverts type apparatus (Checchetto et al, Meas Sci Technol., 2004, 15, 127-130). After degassing at room temperature, the hydrogen absorption / desorption properties of the tested samples were calculated by volumetric measurement using the ideal gas law. The hydrogen desorption capacity of the samples was measured every 50 ° C between 50 ° C and 500 ° C. For each temperature, the measurement of the hydrogen desorption capacity was determined after a total desorption time of 2 hours. The calibrated volume, in which the hydrogen was collected, was regularly emptied so as to maintain a pressure always lower than 1 bar. The samples were rehydrogenated under a pressure of 100 bar of hydrogen at 400 ° C for 12 hours.
• the delay ⁇ was synchronized with the rotation frequency and a ls recycle time was used.
• silica monoliths thus synthesized were then washed three times for 24 hours with a THF / acetone mixture (50/50: v / v) in order to extract the oily phase.
• the silica monolith was then allowed to dry for one week at room temperature and then subjected to heat treatment at 650 ° C for 6 hours applying a rate of rise in temperature of 2 ° C / min. first tray at 200 ° C for 2 hours.
• Silica monoliths were obtained which were designated MSi.
• the MSi silica monoliths obtained above were immersed in Solution S25 in a beaker.
• the beakers were placed under dynamic vacuum until disappearance of the effervescence to ensure a good impregnation of the silica matrices by the phenolic resin solutions, and then left under static vacuum for 3 days.
• the silica monoliths thus impregnated with Solution S25 were then washed rapidly with THF and then dried in an oven at a temperature of 80 ° C. for 24 hours in order to facilitate the evaporation of the solvent and thermally initiate the crosslinking of the monomers of the phenolic resin.
• the MSIS25 monoliths were then subjected to a second heat treatment in a hot air oven, at 155 ° C for 5 hours, with a temperature rise rate of 2 ° C / min., making a first tray at 80 ° C for 12 hours and then a second tray at 1 10 ° C for 3 hours.
• the monoliths were then allowed to return to room temperature simply by stopping the oven.
• the monoliths were then washed with 10% hydrofluoric acid in order to eliminate the silica impression, then rinsed abundantly with distilled water for 24 hours.
• the graphitized carbon monoliths thus obtained was designated MS25carb.
• MS25carb monoliths obtained above in the previous step were immersed in a beaker containing a solution of palladium chloride at 4.5 ⁇ 10 -2 M in acetone / water (1: 1; v: v) acidified with water. 5 ml of hydrochloric acid
• the beaker was then placed under dynamic vacuum until disappearance of the effervescence so as to ensure the good impregnation of the palladium chloride solution in the porosity of the monoliths, then left under Static vacuum for 3 days
• the monoliths were then dried in air, then the palladium chloride was reduced by heat treatment of the monoliths at 400 ° C. (rate of rise in temperature 2 ° C./min) under hydrogen.
• Composite monoliths thus obtained were named PdMS25carb.
• MS25carb monoliths obtained above in the previous step were immersed in a beaker containing a solution of 4.5.10 "2 M potassium tetrachloroaurate in acetone / water (1: 1; v: v). was then placed under dynamic vacuum until disappearance of the effervescence so as to ensure the good impregnation of the potassium tetrachloroaurate solution in the porosity of the monoliths, then left under static vacuum for 3 days. then air-dried, and the potassium tetrachloroaurate Au 3 + ions were reduced by heat treatment of the monoliths at 80 ° C. under a hydrogen pressure of 8 bars, The composite monoliths thus obtained were called AuMS25carb. 4) Characterizations
• FIG. 1 shows a macroscopic view of an MS25carb monolith obtained at the end of the second stage of the process.
• FIG. 2 shows a microscopic view at the SEM of the macroscopic gate array of the MS25carb carbon monolith of FIG. 1.
• the monolith comprises an open macroporosity whose texture resembles an aggregate of hollow spheres.
• FIG. attached figure 3 corresponds to the PdMS25carb monolith and Figure 3b to the AuMS25carb monolith. It is found that the distribution of the metallic nanoparticles is fairly homogeneous from the outside to the inside of the monolith with some aggregates
• the results of the mercury intrusion measurements carried out on the PdMS25carb and AuMS25carb monoliths synthesized in this example are shown in the appended FIG. 4.
• the intrusion volume (in ml / g / ⁇ ) is a function of the pore diameter (in ⁇ ), FIG. 4a corresponding to the PdMS25carb monolith and FIG. 4b to the AuMS25carb monolith. It is important to emphasize here that mercury intrusion measurements can only determine the diameter of the windows that connect two adjacent hollow spheres and not the hollow spheres themselves. It is observed that the diameter of these windows is polydisperse and has a bimodal distribution.
• the specific surface of the monolith comprising gold nanoparticles is smaller than that of the monolith comprising nanoparticles of palladium.
• the gold nanoparticles are smaller than the palladium nanoparticles and are therefore distributed more homogeneously on the surface of the macropores. This has the effect of minimizing the diffusion of nitrogen through the porosity.
• the porosity is expressed in m 2 .g -1 , that is to say that for the same intrinsic porosity, the monolith comprising the most metal nanoparticles intrinsically have a lower surface area.
• the monoliths thus prepared do not include a mesoporous network.
• Elemental analyzes of the PdMS25carb and AuMS25carb monoliths indicate that they contain respectively 8.15% palladium and 10.07% gold.
• FIG. 5 The XPS spectra of the PdMS25carb and AuMS25carb monoliths are given in the appended FIG. 5 on which the binding energy (in eV) is a function of the number of strokes (in Arbitrary Units: AU); FIG. 5a corresponding to the PdMS25carb monolith based on the binding energy of the metallic palladium and FIG. 5b to the AuMS25carb monolith based on the binding energy of the metallic gold.
• the spectrum of FIG. 5a shows the peaks of Pd 3d 5/2 at 340.3 eV and Pd 3d 7/2 at 335.5 eV corresponding to palladium metal, that is to say to palladium at zero oxidation state.
• a slight shoulder indicated by the arrows on each of the peaks may also be observed at a slightly higher binding energy value, said shoulder being attributed to the presence of a small amount of palladium oxide PdO, this amount being however too weak to affect the performance of the monolith vis-à-vis the subsequent storage of hydrogen.
• the peaks of the metallic gold 4F 7/2 and 4F 5/2 are observed at 83.6 eV and 87.5 eV respectively, these peaks being significant for a total reduction of the gold present in the monolith in the state of zero oxidation.
• the carbon monoliths PdMS25carb and AuMS25carb prepared above in Example 1 were used to store hydrogen, by heterogeneous nucleation of LiBH 4 within the micropores. The release of hydrogen from carbon monoliths has also been studied.
• the amount of LiBH 4 loaded into the monoliths was determined by measuring the Li content by atomic absorption spectroscopy (AAS) on a spectrometer sold under the trade name AAnalyst 300 by the company PerkinElmer, after dissolution of the LiBH loaded monoliths. 4 in a solution of 1.0 M hydrochloric acid.
• AAS atomic absorption spectroscopy
• 50 mg of monolith loaded with LiBH 4 are introduced into a flask containing 250 cm 3 of 0.1 M HCl solution, and then the flask is placed in an ultrasonic tank for duration of 30 minutes.
• the solution obtained is assayed by atomic absorption spectrometry. Standard solutions at 1, 2 and 3 mg.L -1 of Li were previously used to calibrate the spectrometer.
• FIG. 6 represents the X-ray diffraction patterns of the PdMS25carb / LiBH 4 and AuMS25carb / LiBH 4 monoliths (curves 4 and 3, respectively), as well as of a carbon monolith unmodified by metallic nanoparticles (MS25carb / LiBH 4 curve 2) and commercial LiBH 4 alone (curve 1).
• the LiBH 4 diffraction peaks are indeed present on the curves 3 and 4 respectively corresponding to the AuMS25carb / LiBH 4 and PdMS25carb / LiBH 4 monoliths.
• the metal nanoparticles present in these monoliths favor the crystallization of LiBH 4 and attenuate the negative influence of the micropores present on the surface of the macropores. This is probably due to the fact that the carbon walls and the metal nanoparticles have different surface energies and consequently a wettability lower than those of the metal nanoparticles vis-à-vis the LiBH 4 solution used to impregnate the monoliths.
• the heterogeneous nucleation of LiBH 4 on the surface of metal nanoparticles is thus favored and since there are fewer nanoparticles present on the macropore surface than micropores, the nucleation of LiBH 4 will be minimized while the crystalline growth will be contrary augmented and optimized so as to consume all of the precursor LiBH 4 present in the impregnating solution.
• the first endothermic peak at 116 ° C indicates that LiBH 4 undergoes a phase transition from low temperature orthorhombic mesh (Pnma) to a high temperature phase (P6 3 mc) (Soulie, J.-P, et al. J. Ail Comp., 2002, 346, 200).
• the second endothermic peak at 286 ° C corresponds to the melting of LiBH 4 .
• FIG. 8 shows the dihydrogen emission curves measured by thermodesorption coupled to the mass spectrometer on the various samples.
• the continuous curve without a symbol corresponds to the emission of dihydrogen measured on LiBH 4 alone
• the curve the line interrupted by empty circles corresponds to the emission of hydrogen measured on the monolith MS25carb / LiBH 4 not according to the invention
• the curve with the trace interrupted by empty squares corresponds to the emission of hydrogen measured on the monolith AuMS25carb / LiBH 4 according to the invention
• the curve with the trace interrupted by empty triangles corresponds to the emission of hydrogen measured on the monolith PdMS25carb / LiBH 4 according to the invention.
• the peak of desorption of dihydrogen observed at 60 ° C with the monoliths according to the invention PdMS25carb / LiBH 4 and AuMS25carb / LiBH 4 are less, suggesting a less important oxidation.
• the main peak of desorption of dihydrogen is centered at 275 ° C and more acute than the corresponding peak observed for the monolith MS25carb / LiBH 4 does not include metal nanoparticles.
• additional desorption is observed at a temperature below 350 ° C, which could correspond to the decomposition of LiH.
• FIG. 9 shows the dihydrogen emission curves obtained by volumetric measurements according to the Sievert method for each of the samples tested.
• the quantity of desorbed hydrogen (in% by weight relative to LiBH 4 ) is a function of the temperature (in C); the curve with the solid squares corresponds to the dihydrogen emission measured from the LiBH 4 alone, that with the empty circles corresponds to the emission of dihydrogen measured from the MS25carb / LiBH 4 monolith containing no metallic nanoparticles, that with the empty squares AuMS25carb monolith / LiBH 4 according to the invention and that with the empty triangles to the monolith PdMS25carb / LiBH 4 according to the invention.
• the values of% mass of desorbed hydrogen given in FIG. 9 must be divided by 5 in order to obtain the% mass of hydrogen desorbed relative to the total mass of materials (including the mass of the matrix of carbon monoliths and that of the metal nanoparticles where appropriate).
• FIG. 10 shows the quantity of hydrogen released at 500 ° C. (in mass%) as a function of the number of cycles during the first 5 cycles of desorption / absorption.
• the curve with the solid squares corresponds to the LiBH 4 alone, that with the empty circles to the MS25carb / LiBH 4 monoliths not in accordance with the invention, that with the empty squares to the AuMS25carb / LiBH 4 monolith according to the invention. and that with the empty triangles with the PdMS25carb / LiBH 4 monolith according to the invention.
• the monoliths in accordance with the invention that is to say having inclusions of metal nanoparticles, a very large increase in the amount of dihydrogen that can be reabsorbed is observed. Indeed, approximately 10.4% dihydrogen mass are salted during the 2nd cycle as well with the monolith AuMS25carb / LiBH 4 with the PdMS25carb / LiBH 4 monolith. The existence of a reversible phenomenon is thus demonstrated, the retention capacity of the dihydrogen of the PdMS25carb / LiBH 4 monolith being slightly greater than that of the AuMS25carb / LiBH 4 monolith. After 5 cycles of desorption / reabsorption, the monolith PdMS25carb / LiBH 4) still allows to release 7.4% by weight of dihydrogen, which corresponds to 48% of the capacity obtained during the first desorption.
• Curve 4 AuMS25carb / LiBH 4 monolith as prepared
• Curve 5 monolith MS25carb / LiBH 4 after 1 desorption / absorption cycle
• Curve 6 monolith PdMS25carb / LiBH 4 after 1 desorption / absorption cycle
• Curve 7 AuMS25carb / LiBH 4 monolith after 1 desorption / absorption cycle
• Curve 8 monolith PdMS25carb / LiBH 4 after 5 cycles of desorption / absorption
• Curve 9 AuMS25carb / LiBH 4 monolith after 5 cycles of desorption / absorption.
• Nanoparticles improves the rehydrogenation process and promotes the formation of a BH 4 type environment.
• Nanoparticles promote heterogeneous nucleation and crystal growth LiBH 4 .
• the metallic nanoparticles because of their greater capacity to absorb heat than the carbon skeleton, offer nanospots having a higher temperature than the carbonaceous surface on which the rehydrogenation kinetics is certainly improved.
• the NMR spectra of n B of the monoliths PdMS25carb / LiBH 4 and AuMS25carb / LiBH 4 according to the invention give an important signal at -41 ppm characteristic of the presence of BH 4 , confirming that hydrogen recombines with boron and that the hydrogen storage method in the monoliths of the invention is well reversible.
• the rehydrogenation performances of the monoliths according to the present invention are very clearly superior to those of the monolith MS25carb / LiBH 4 not comprising any inclusion of metal nanoparticles.

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